The invention pertains to a rotatable cutting bit which mounts to a stationary block on a rotatable drum wherein the bit impinges a substrate upon the rotation of the drum. More specifically, the invention pertains to the aforementioned type of bit which includes a replaceable head portion.
Rotatable cutting bits typically comprise a consumable portion of a complete cutting apparatus, such as, for example, a road planing machine or a coal mining machine. Broadly speaking, such a rotatable cutting bit comprises a unitary steel shank having a hard cutting insert at the forward end thereof and a retaining assembly at the rearward end thereof.
The shank mounts in the bore of a stationary block on a rotatable drum by means of a retainer assembly so that the cutting bit is rotatable relative to the block. U.S Pat. No. 4,201,421 to DenBesten et al. shows the use of a smooth sleeve to retain the mining bit within the bore of a block through frictional engagement between the sleeve retainer and the wall of the bore. U.S. Pat. No. 3,519,309 to Engle et al. shows the use of a dimple clip to rotatably connect a mining bit to a block. FIGS. 8 and 11 shows two embodiments where the radially outward projections of the dimple clip (FIG. 10) engage a channel or the like to retain the bit within the bore of the block. The same feature is present in FIG. 1 of U.S. Pat. No. 3,752,515 to Oaks et al.
In operation, the drum rotates so as to drive the cutting bit into the substrate whereby the hard cutting insert and the forward portion of the unitary steel shank experience the maximum amount of wear. Furthermore, the rotatable cutting bit rotates in the bore of the block so that both the rearward end of the shank and the wall of the bore experience wear.
Once the forward portion of the cutting bit wears to a point where it no longer is substantively effective, the operator of the cutting apparatus must replace the complete worn cutting bit with a complete new cutting bit. Typically, the operator removes the worn bits by using a pry bar to pry the bit out of the bore of the block or a pneumatic hammer to impact the bit out of the bore of the block. It is typically the case that the operator then discards the complete worn bit.
Eventually, the rotation of the cutting bit in the bore of the block causes the bore to wear to such an extent that the operator must replace the block. To replace the block, which is typically welded to the drum, the operator must remove the welded block from the drum and weld a new block to the drum. Such replacement of one or more blocks is a time-consuming activity which typically causes the operator to lose valuable operating time.
Thus, it would be highly desirable to provide a rotatable cutting bit that minimizes the costs involved with the replacement of worn cutting bits.
It would be highly desirable to provide a rotatable cutting bit that does not require the discarding of the complete cutting bit once the forward portion thereof has become worn.
It would be highly desirable to provide a rotatable cutting bit that minimizes the wear to the bore of the block caused by the rotation of the rotatable cutting bit.